[PATCH] FAT: Allow 0xE9 near jump in fat_read_static_bpb()

[PATCH] FAT: Allow 0xE9 near jump in fat_read_static_bpb()

[Ziran Zhang]

The fat_read_static_bpb() only accepts a short jump as a valid
bootstrap code signature for DOS 1.x volumes when the dos1xfloppy
mount option is used.

However, according to the Microsoft fatgen103.doc, the BS_jmpBoot
field has two allowed forms: 0xEB 0x?? 0x90 (short jump + NOP)
and 0xE9 0x?? 0x?? (near jump). The specification explicitly states
that either form is acceptable.

This patch relaxes the check to also accept 0xE9 as the first byte of
the jump instruction.

Signed-off-by: Ziran Zhang <zhangcoder@yeah.net>
---
 fs/fat/inode.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/fat/inode.c b/fs/fat/inode.c
index 28f78df08..0f64552e2 100644
--- a/fs/fat/inode.c
+++ b/fs/fat/inode.c
@@ -1479,8 +1479,8 @@ static int fat_read_static_bpb(struct super_block *sb,
 	int error = -EINVAL;
 	unsigned i;
 
-	/* 16-bit DOS 1.x reliably wrote bootstrap short-jmp code */
-	if (b->ignored[0] != 0xeb || b->ignored[2] != 0x90) {
+	/* 16-bit DOS 1.x reliably wrote bootstrap short-jmp or near-jmp code */
+	if ((b->ignored[0] != 0xeb || b->ignored[2] != 0x90) && (b->ignored[0] != 0xe9)) {
 		if (!silent)
 			fat_msg(sb, KERN_ERR,
 				"%s; no bootstrapping code", notdos1x);
-- 
2.43.0

Re: [PATCH] FAT: Allow 0xE9 near jump in fat_read_static_bpb()

[OGAWA Hirofumi]

Ziran Zhang <zhangcoder@yeah.net> writes:

> The fat_read_static_bpb() only accepts a short jump as a valid
> bootstrap code signature for DOS 1.x volumes when the dos1xfloppy
> mount option is used.
>
> However, according to the Microsoft fatgen103.doc, the BS_jmpBoot
> field has two allowed forms: 0xEB 0x?? 0x90 (short jump + NOP)
> and 0xE9 0x?? 0x?? (near jump). The specification explicitly states
> that either form is acceptable.
>
> This patch relaxes the check to also accept 0xE9 as the first byte of
> the jump instruction.
>
> Signed-off-by: Ziran Zhang <zhangcoder@yeah.net>
> ---
>  fs/fat/inode.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/fs/fat/inode.c b/fs/fat/inode.c
> index 28f78df08..0f64552e2 100644
> --- a/fs/fat/inode.c
> +++ b/fs/fat/inode.c
> @@ -1479,8 +1479,8 @@ static int fat_read_static_bpb(struct super_block *sb,
>  	int error = -EINVAL;
>  	unsigned i;
>  
> -	/* 16-bit DOS 1.x reliably wrote bootstrap short-jmp code */
> -	if (b->ignored[0] != 0xeb || b->ignored[2] != 0x90) {
> +	/* 16-bit DOS 1.x reliably wrote bootstrap short-jmp or near-jmp code */
> +	if ((b->ignored[0] != 0xeb || b->ignored[2] != 0x90) && (b->ignored[0] != 0xe9)) {

Looks like over 80 columns.

	if ((b->ignored[0] != 0xeb || b->ignored[2] != 0x90) &&
	    (b->ignored[0] != 0xe9)) {

or such please.

Thanks.

>  		if (!silent)
>  			fat_msg(sb, KERN_ERR,
>  				"%s; no bootstrapping code", notdos1x);

-- 
OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>

[PATCH v2 v2] FAT: Allow 0xE9 near jump in fat_read_static_bpb()

[Ziran Zhang]

> Looks like over 80 columns.
>
> 	if ((b->ignored[0] != 0xeb || b->ignored[2] != 0x90) &&
> 	    (b->ignored[0] != 0xe9)) {
>
> or such please.
>
> Thanks.

Thank you for the review. I have fixed the line length and sent v2 patch.

Signed-off-by: Ziran Zhang <zhangcoder@yeah.net>
---
 fs/fat/inode.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/fat/inode.c b/fs/fat/inode.c
index 28f78df08..0e7d106ea 100644
--- a/fs/fat/inode.c
+++ b/fs/fat/inode.c
@@ -1479,8 +1479,9 @@ static int fat_read_static_bpb(struct super_block *sb,
 	int error = -EINVAL;
 	unsigned i;
 
-	/* 16-bit DOS 1.x reliably wrote bootstrap short-jmp code */
-	if (b->ignored[0] != 0xeb || b->ignored[2] != 0x90) {
+	/* 16-bit DOS 1.x reliably wrote bootstrap short-jmp or near-jmp code */
+	if ((b->ignored[0] != 0xeb || b->ignored[2] != 0x90) &&
+	    (b->ignored[0] != 0xe9)) {
 		if (!silent)
 			fat_msg(sb, KERN_ERR,
 				"%s; no bootstrapping code", notdos1x);
-- 
2.43.0

[PATCH v3] FAT: Allow 0xE9 near jump in fat_read_static_bpb()

[Ziran Zhang]

Changes in v3:
- Fix line length over 80 columns (split condition into two lines)
- Correct version number from erroneous "v2 v2" to v3

Signed-off-by: Ziran Zhang <zhangcoder@yeah.net>
---

Please ignore the earlier erroneous "[PATCH v2 v2]" patch. 
This is the corrected v3.

 fs/fat/inode.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/fat/inode.c b/fs/fat/inode.c
index 28f78df08..0e7d106ea 100644
--- a/fs/fat/inode.c
+++ b/fs/fat/inode.c
@@ -1479,8 +1479,9 @@ static int fat_read_static_bpb(struct super_block *sb,
 	int error = -EINVAL;
 	unsigned i;
 
-	/* 16-bit DOS 1.x reliably wrote bootstrap short-jmp code */
-	if (b->ignored[0] != 0xeb || b->ignored[2] != 0x90) {
+	/* 16-bit DOS 1.x reliably wrote bootstrap short-jmp or near-jmp code */
+	if ((b->ignored[0] != 0xeb || b->ignored[2] != 0x90) &&
+	    (b->ignored[0] != 0xe9)) {
 		if (!silent)
 			fat_msg(sb, KERN_ERR,
 				"%s; no bootstrapping code", notdos1x);
-- 
2.43.0

Re: [PATCH v3] FAT: Allow 0xE9 near jump in fat_read_static_bpb()

[OGAWA Hirofumi]

Ziran Zhang <zhangcoder@yeah.net> writes:

> Changes in v3:
> - Fix line length over 80 columns (split condition into two lines)
> - Correct version number from erroneous "v2 v2" to v3
>
> Signed-off-by: Ziran Zhang <zhangcoder@yeah.net>

Could you add original commit log, instead of changelog?

Thanks.

> ---
>
> Please ignore the earlier erroneous "[PATCH v2 v2]" patch. 
> This is the corrected v3.
>
>  fs/fat/inode.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/fs/fat/inode.c b/fs/fat/inode.c
> index 28f78df08..0e7d106ea 100644
> --- a/fs/fat/inode.c
> +++ b/fs/fat/inode.c
> @@ -1479,8 +1479,9 @@ static int fat_read_static_bpb(struct super_block *sb,
>  	int error = -EINVAL;
>  	unsigned i;
>  
> -	/* 16-bit DOS 1.x reliably wrote bootstrap short-jmp code */
> -	if (b->ignored[0] != 0xeb || b->ignored[2] != 0x90) {
> +	/* 16-bit DOS 1.x reliably wrote bootstrap short-jmp or near-jmp code */
> +	if ((b->ignored[0] != 0xeb || b->ignored[2] != 0x90) &&
> +	    (b->ignored[0] != 0xe9)) {
>  		if (!silent)
>  			fat_msg(sb, KERN_ERR,
>  				"%s; no bootstrapping code", notdos1x);

-- 
OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>

[PATCH v4] FAT: Allow 0xE9 near jump in fat_read_static_bpb()

[Ziran Zhang]

The fat_read_static_bpb() only accepts a short jump as a valid
bootstrap code signature for DOS 1.x volumes when the dos1xfloppy
mount option is used.

However, according to the Microsoft fatgen103.doc, the BS_jmpBoot
field has two allowed forms: 0xEB 0x?? 0x90 (short jump + NOP)
and 0xE9 0x?? 0x?? (near jump). The specification explicitly states
that either form is acceptable.

This patch relaxes the check to also accept 0xE9 as the first byte of
the jump instruction.

Changes in v4:
- Add original commit log

Signed-off-by: Ziran Zhang <zhangcoder@yeah.net>
---

> Could you add original commit log, instead of changelog?
> 
> Thanks.

Done! Please ignore the earlier erroneous v2 v2 and v3.

 fs/fat/inode.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/fs/fat/inode.c b/fs/fat/inode.c
index 28f78df08..0e7d106ea 100644
--- a/fs/fat/inode.c
+++ b/fs/fat/inode.c
@@ -1479,8 +1479,9 @@ static int fat_read_static_bpb(struct super_block *sb,
 	int error = -EINVAL;
 	unsigned i;
 
-	/* 16-bit DOS 1.x reliably wrote bootstrap short-jmp code */
-	if (b->ignored[0] != 0xeb || b->ignored[2] != 0x90) {
+	/* 16-bit DOS 1.x reliably wrote bootstrap short-jmp or near-jmp code */
+	if ((b->ignored[0] != 0xeb || b->ignored[2] != 0x90) &&
+	    (b->ignored[0] != 0xe9)) {
 		if (!silent)
 			fat_msg(sb, KERN_ERR,
 				"%s; no bootstrapping code", notdos1x);
-- 
2.43.0

Re: [PATCH v4] FAT: Allow 0xE9 near jump in fat_read_static_bpb()

[OGAWA Hirofumi]

Ziran Zhang <zhangcoder@yeah.net> writes:

> The fat_read_static_bpb() only accepts a short jump as a valid
> bootstrap code signature for DOS 1.x volumes when the dos1xfloppy
> mount option is used.
>
> However, according to the Microsoft fatgen103.doc, the BS_jmpBoot
> field has two allowed forms: 0xEB 0x?? 0x90 (short jump + NOP)
> and 0xE9 0x?? 0x?? (near jump). The specification explicitly states
> that either form is acceptable.
>
> This patch relaxes the check to also accept 0xE9 as the first byte of
> the jump instruction.
>
> Changes in v4:
> - Add original commit log
>
> Signed-off-by: Ziran Zhang <zhangcoder@yeah.net>

Thanks.

Acked-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>

> ---
>
>> Could you add original commit log, instead of changelog?
>> 
>> Thanks.
>
> Done! Please ignore the earlier erroneous v2 v2 and v3.
>
>  fs/fat/inode.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/fs/fat/inode.c b/fs/fat/inode.c
> index 28f78df08..0e7d106ea 100644
> --- a/fs/fat/inode.c
> +++ b/fs/fat/inode.c
> @@ -1479,8 +1479,9 @@ static int fat_read_static_bpb(struct super_block *sb,
>  	int error = -EINVAL;
>  	unsigned i;
>  
> -	/* 16-bit DOS 1.x reliably wrote bootstrap short-jmp code */
> -	if (b->ignored[0] != 0xeb || b->ignored[2] != 0x90) {
> +	/* 16-bit DOS 1.x reliably wrote bootstrap short-jmp or near-jmp code */
> +	if ((b->ignored[0] != 0xeb || b->ignored[2] != 0x90) &&
> +	    (b->ignored[0] != 0xe9)) {
>  		if (!silent)
>  			fat_msg(sb, KERN_ERR,
>  				"%s; no bootstrapping code", notdos1x);

-- 
OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>